This invention relates to a hydroprocessing catalyst and its use for hydroprocessing hydrocarbon-containing oils.
In the refining of hydrocarbon oils, it is often desirable to subject the hydrocarbon oil to catalytic hydroprocessing. During hydroprocessing, particulate catalysts are utilized to promote reactions such as desulfurization, denitrogenation, demetallization and/or conversion of asphaltene compounds. This is accomplished by contacting the particulate catalyst with a feedstock, such as a vacuum gas oil residual petroleum oil fraction, under conditions of elevated temperature and pressure and in the presence of hydrogen so that the sulfur components are converted to hydrogen sulfide, nitrogen components to ammonia, asphaltenes to molecules having increased hydrogen to carbon (H/C) ratios and contaminant metal components to components capable of being deposited on the catalyst. Typically, hydroprocessing is employed to reduce the concentration of nitrogen and sulfur in feedstocks so as to produce hydrocarbons which, when eventually combusted, result in reduced air pollutants of the forms NO.sub.x and SO.sub.x. Reducing the concentration of nitrogen and metals is also desirable to protect other refining catalysts, such as hydrocracking catalysts, which deactivate in the presence of nitrogen and contaminant metals.
A typical hydroprocessing catalyst contains hydrogenation metals on a porous refractory oxide support. Hydrogenation metals usually include Group VIB and/or Group VIII active metal components supported on amorphous refractory oxide supports such as alumina. Also, phosphorus components have been incorporated in such catalysts. One group of hydroprocessing catalysts which have provided excellent service to petroleum refiners is a nickel-phosphorus-molybdenum-containing catalyst, commonly called a "Ni-P-Mo" catalyst. The porous refractory oxide supports of such catalysts have a wide variety of pore sizes and pore size distributions. Recently, active and stable Ni-P-Mo catalysts having particularly narrow pore size distributions have been useful in hydroprocessing hydrocarbons. For example, U.S. Pat. No. 4,500,424 issued to Simpson et al. discloses a Ni-P-Mo catalyst having a pore size distribution including at least 75 percent of the pore volume in pores of diameter from about 70 to about 130 angstroms, and further containing less than 10 percent of the total pore volume in pores of diameter less than 70 angstroms. During recent years, industrial use has been made of Ni-P-Mo catalysts having high contents of molybdenum, i.e., at least equal to 25 weight percent, calculated as MoO.sub.3, and having narrow pore size distributions similar to those disclosed in U.S. Pat. No. 4,500,424, but containing more than 10 percent of the total pore volume in pores of diameter less than 70 angstroms.
Despite the high hydroprocessing activity of the catalysts of the prior art, catalysts of yet higher activities and/or stabilities are still being sought. The higher the activity of the catalyst, the lower the reactor temperature required to obtain a product of given nitrogen, sulfur, asphaltene, or metal content from the feedstock. The lower the reaction temperature, the lower the expense of hydroprocessing a given unit of feedstock due to savings in process heat requirement. Furthermore, hydroprocessing at a lower reaction temperature usually extends the life of the catalyst, i.e., increases catalyst stability, assuming, of course, that all other process parameters are held constant.
Accordingly, it is a major object of the invention to provide an improved hydroprocessing catalyst, and particularly, an improved hydroprocessing catalyst relative to known comparable catalysts.
A further object is to provide a process for hydrodesulfurizing or hydrodenitrogenating a hydrocarbon feedstock containing a relatively low content of organometallic components.
These and other objects and advantages of the invention will become apparent from the following description.